My present invention relates generally to information transmission systems. More particularly, the invention relates to an optical color communication system.
It is well known in the field of communications that the shorter is the wavelength of the carrier signal for data or information transmission, the higher is the potential data transfer rate. This has given emphasis to the consideration of optical communication systems for achieving high data transfer rates. There is also negligible leakage of information in an optical communication system due to the low sidelobe amplitudes of the transmitter of an optical beam. This results in security of transmission. Since there is no interaction or interference between optical (light) frequency transmissions and radio frequency transmissions due to the vast differences in their frequencies and wavelengths, radio frequency pollution (i.e., the overcrowding and resultant interference between radio frequency communication channels) is not increased.
In recent optical communication systems, a laser has been utilized as the carrier. Single channel systems are, however, obtained. The high carrier frequency afforded by the laser, typically about 10.sup.14 hertz, does permit many low data rate channels to be temporally multiplexed into the single channel. A relatively large amount of electrooptical apparatus is, however, required to multiplex the low data rate channels off and on the single high data rate channel. At present, a suitable laser modulator/demodulator which works effectively at a gigahertz (10.sup.9 hertz) is still a major development item.
To code a high density data storage medium such as a photograph for transmission of the data, it is ordinarily necessary to scan the photograph with a single spot of light. The output of a detector which receives the modulated scan spot as its light intensity varies during scan is processed electronically and coded for transmission. Where the data to be transmitted is in a single color, the variation of tone (as in a black and white photograph) can be coded as a digital signal having a bit stream variable with tone or as an analogue signal generated according to the variation in a laser characteristic such as amplitude, phase or polarization angle. If the data is in a multicolored form such as a Kodachrome transparency, it is necessary to have three channels for the three primary colors and which would carry respective amounts of the primary colors in each resolved bit of the color record as it is scanned. At the receiver, the transmitted data is suitably decoded and processed into an appropriate form for subsequent handling. This usually involves another scanning operation over a magnetic tape or a radiation sensitive film having the decoded data recorded thereon.
It has been further estimated that an intercity information system, for example, will have to carry more than 10.sup.10 bits per second of data or information in order to justify its installation cost. An optical color communication system is highly desirable over conventional radio or video frequency communication systems because the optical system is very much simpler, less costly, more reliable, requires less maintenance and provides a data transfer rate far beyond the capability of the radio or video frequency communication systems.